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  <section id="coroutines-and-tasks">
<h1>Coroutines and Tasks<a class="headerlink" href="#coroutines-and-tasks" title="Permalink to this headline">¶</a></h1>
<p>This section outlines high-level asyncio APIs to work with coroutines
and Tasks.</p>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><p><a class="reference internal" href="#coroutines" id="id1">Coroutines</a></p></li>
<li><p><a class="reference internal" href="#awaitables" id="id2">Awaitables</a></p></li>
<li><p><a class="reference internal" href="#running-an-asyncio-program" id="id3">Running an asyncio Program</a></p></li>
<li><p><a class="reference internal" href="#creating-tasks" id="id4">Creating Tasks</a></p></li>
<li><p><a class="reference internal" href="#sleeping" id="id5">Sleeping</a></p></li>
<li><p><a class="reference internal" href="#running-tasks-concurrently" id="id6">Running Tasks Concurrently</a></p></li>
<li><p><a class="reference internal" href="#shielding-from-cancellation" id="id7">Shielding From Cancellation</a></p></li>
<li><p><a class="reference internal" href="#timeouts" id="id8">Timeouts</a></p></li>
<li><p><a class="reference internal" href="#waiting-primitives" id="id9">Waiting Primitives</a></p></li>
<li><p><a class="reference internal" href="#running-in-threads" id="id10">Running in Threads</a></p></li>
<li><p><a class="reference internal" href="#scheduling-from-other-threads" id="id11">Scheduling From Other Threads</a></p></li>
<li><p><a class="reference internal" href="#introspection" id="id12">Introspection</a></p></li>
<li><p><a class="reference internal" href="#task-object" id="id13">Task Object</a></p></li>
<li><p><a class="reference internal" href="#generator-based-coroutines" id="id14">Generator-based Coroutines</a></p></li>
</ul>
</div>
<section id="coroutines">
<span id="coroutine"></span><h2><a class="toc-backref" href="#id1">Coroutines</a><a class="headerlink" href="#coroutines" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="../glossary.html#term-coroutine"><span class="xref std std-term">Coroutines</span></a> declared with the async/await syntax is the
preferred way of writing asyncio applications.  For example, the following
snippet of code (requires Python 3.7+) prints “hello”, waits 1 second,
and then prints “world”:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">asyncio</span>

<span class="gp">&gt;&gt;&gt; </span><span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="gp">... </span>    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;hello&#39;</span><span class="p">)</span>
<span class="gp">... </span>    <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="gp">... </span>    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;world&#39;</span><span class="p">)</span>

<span class="gp">&gt;&gt;&gt; </span><span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
<span class="go">hello</span>
<span class="go">world</span>
</pre></div>
</div>
<p>Note that simply calling a coroutine will not schedule it to
be executed:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="n">main</span><span class="p">()</span>
<span class="go">&lt;coroutine object main at 0x1053bb7c8&gt;</span>
</pre></div>
</div>
<p>To actually run a coroutine, asyncio provides three main mechanisms:</p>
<ul>
<li><p>The <a class="reference internal" href="#asyncio.run" title="asyncio.run"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.run()</span></code></a> function to run the top-level
entry point “main()” function (see the above example.)</p></li>
<li><p>Awaiting on a coroutine.  The following snippet of code will
print “hello” after waiting for 1 second, and then print “world”
after waiting for <em>another</em> 2 seconds:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">time</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">say_after</span><span class="p">(</span><span class="n">delay</span><span class="p">,</span> <span class="n">what</span><span class="p">):</span>
    <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="n">delay</span><span class="p">)</span>
    <span class="nb">print</span><span class="p">(</span><span class="n">what</span><span class="p">)</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;started at </span><span class="si">{</span><span class="n">time</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%X</span><span class="s1">&#39;</span><span class="p">)</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>

    <span class="k">await</span> <span class="n">say_after</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="s1">&#39;hello&#39;</span><span class="p">)</span>
    <span class="k">await</span> <span class="n">say_after</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="s1">&#39;world&#39;</span><span class="p">)</span>

    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;finished at </span><span class="si">{</span><span class="n">time</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%X</span><span class="s1">&#39;</span><span class="p">)</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<p>Expected output:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">started</span> <span class="n">at</span> <span class="mi">17</span><span class="p">:</span><span class="mi">13</span><span class="p">:</span><span class="mi">52</span>
<span class="n">hello</span>
<span class="n">world</span>
<span class="n">finished</span> <span class="n">at</span> <span class="mi">17</span><span class="p">:</span><span class="mi">13</span><span class="p">:</span><span class="mi">55</span>
</pre></div>
</div>
</li>
<li><p>The <a class="reference internal" href="#asyncio.create_task" title="asyncio.create_task"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.create_task()</span></code></a> function to run coroutines
concurrently as asyncio <a class="reference internal" href="#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">Tasks</span></code></a>.</p>
<p>Let’s modify the above example and run two <code class="docutils literal notranslate"><span class="pre">say_after</span></code> coroutines
<em>concurrently</em>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="n">task1</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span>
        <span class="n">say_after</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="s1">&#39;hello&#39;</span><span class="p">))</span>

    <span class="n">task2</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span>
        <span class="n">say_after</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="s1">&#39;world&#39;</span><span class="p">))</span>

    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;started at </span><span class="si">{</span><span class="n">time</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%X</span><span class="s1">&#39;</span><span class="p">)</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>

    <span class="c1"># Wait until both tasks are completed (should take</span>
    <span class="c1"># around 2 seconds.)</span>
    <span class="k">await</span> <span class="n">task1</span>
    <span class="k">await</span> <span class="n">task2</span>

    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;finished at </span><span class="si">{</span><span class="n">time</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%X</span><span class="s1">&#39;</span><span class="p">)</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>
</pre></div>
</div>
<p>Note that expected output now shows that the snippet runs
1 second faster than before:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">started</span> <span class="n">at</span> <span class="mi">17</span><span class="p">:</span><span class="mi">14</span><span class="p">:</span><span class="mi">32</span>
<span class="n">hello</span>
<span class="n">world</span>
<span class="n">finished</span> <span class="n">at</span> <span class="mi">17</span><span class="p">:</span><span class="mi">14</span><span class="p">:</span><span class="mi">34</span>
</pre></div>
</div>
</li>
</ul>
</section>
<section id="awaitables">
<span id="asyncio-awaitables"></span><h2><a class="toc-backref" href="#id2">Awaitables</a><a class="headerlink" href="#awaitables" title="Permalink to this headline">¶</a></h2>
<p>We say that an object is an <strong>awaitable</strong> object if it can be used
in an <a class="reference internal" href="../reference/expressions.html#await"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">await</span></code></a> expression.  Many asyncio APIs are designed to
accept awaitables.</p>
<p>There are three main types of <em>awaitable</em> objects:
<strong>coroutines</strong>, <strong>Tasks</strong>, and <strong>Futures</strong>.</p>
<p class="rubric">Coroutines</p>
<p>Python coroutines are <em>awaitables</em> and therefore can be awaited from
other coroutines:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">nested</span><span class="p">():</span>
    <span class="k">return</span> <span class="mi">42</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Nothing happens if we just call &quot;nested()&quot;.</span>
    <span class="c1"># A coroutine object is created but not awaited,</span>
    <span class="c1"># so it *won&#39;t run at all*.</span>
    <span class="n">nested</span><span class="p">()</span>

    <span class="c1"># Let&#39;s do it differently now and await it:</span>
    <span class="nb">print</span><span class="p">(</span><span class="k">await</span> <span class="n">nested</span><span class="p">())</span>  <span class="c1"># will print &quot;42&quot;.</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<div class="admonition important">
<p class="admonition-title">Important</p>
<p>In this documentation the term “coroutine” can be used for
two closely related concepts:</p>
<ul class="simple">
<li><p>a <em>coroutine function</em>: an <a class="reference internal" href="../reference/compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> function;</p></li>
<li><p>a <em>coroutine object</em>: an object returned by calling a
<em>coroutine function</em>.</p></li>
</ul>
</div>
<p>asyncio also supports legacy <a class="reference internal" href="#asyncio-generator-based-coro"><span class="std std-ref">generator-based</span></a> coroutines.</p>
<p class="rubric">Tasks</p>
<p><em>Tasks</em> are used to schedule coroutines <em>concurrently</em>.</p>
<p>When a coroutine is wrapped into a <em>Task</em> with functions like
<a class="reference internal" href="#asyncio.create_task" title="asyncio.create_task"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.create_task()</span></code></a> the coroutine is automatically
scheduled to run soon:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">nested</span><span class="p">():</span>
    <span class="k">return</span> <span class="mi">42</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Schedule nested() to run soon concurrently</span>
    <span class="c1"># with &quot;main()&quot;.</span>
    <span class="n">task</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span><span class="n">nested</span><span class="p">())</span>

    <span class="c1"># &quot;task&quot; can now be used to cancel &quot;nested()&quot;, or</span>
    <span class="c1"># can simply be awaited to wait until it is complete:</span>
    <span class="k">await</span> <span class="n">task</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<p class="rubric">Futures</p>
<p>A <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> is a special <strong>low-level</strong> awaitable object that
represents an <strong>eventual result</strong> of an asynchronous operation.</p>
<p>When a Future object is <em>awaited</em> it means that the coroutine will
wait until the Future is resolved in some other place.</p>
<p>Future objects in asyncio are needed to allow callback-based code
to be used with async/await.</p>
<p>Normally <strong>there is no need</strong> to create Future objects at the
application level code.</p>
<p>Future objects, sometimes exposed by libraries and some asyncio
APIs, can be awaited:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="k">await</span> <span class="n">function_that_returns_a_future_object</span><span class="p">()</span>

    <span class="c1"># this is also valid:</span>
    <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">gather</span><span class="p">(</span>
        <span class="n">function_that_returns_a_future_object</span><span class="p">(),</span>
        <span class="n">some_python_coroutine</span><span class="p">()</span>
    <span class="p">)</span>
</pre></div>
</div>
<p>A good example of a low-level function that returns a Future object
is <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.run_in_executor" title="asyncio.loop.run_in_executor"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.run_in_executor()</span></code></a>.</p>
</section>
<section id="running-an-asyncio-program">
<h2><a class="toc-backref" href="#id3">Running an asyncio Program</a><a class="headerlink" href="#running-an-asyncio-program" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.run">
<code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">run</code><span class="sig-paren">(</span><em class="sig-param">coro</em>, <em class="sig-param">*</em>, <em class="sig-param">debug=False</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.run" title="Permalink to this definition">¶</a></dt>
<dd><p>Execute the <a class="reference internal" href="../glossary.html#term-coroutine"><span class="xref std std-term">coroutine</span></a> <em>coro</em> and return the result.</p>
<p>This function runs the passed coroutine, taking care of
managing the asyncio event loop, <em>finalizing asynchronous
generators</em>, and closing the threadpool.</p>
<p>This function cannot be called when another asyncio event loop is
running in the same thread.</p>
<p>If <em>debug</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code>, the event loop will be run in debug mode.</p>
<p>This function always creates a new event loop and closes it at
the end.  It should be used as a main entry point for asyncio
programs, and should ideally only be called once.</p>
<p>Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;hello&#39;</span><span class="p">)</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.9: </span>Updated to use <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.shutdown_default_executor" title="asyncio.loop.shutdown_default_executor"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.shutdown_default_executor()</span></code></a>.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The source code for <code class="docutils literal notranslate"><span class="pre">asyncio.run()</span></code> can be found in
<a class="reference external" href="https://github.com/python/cpython/tree/3.9/Lib/asyncio/runners.py">Lib/asyncio/runners.py</a>.</p>
</div>
</dd></dl>

</section>
<section id="creating-tasks">
<h2><a class="toc-backref" href="#id4">Creating Tasks</a><a class="headerlink" href="#creating-tasks" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.create_task">
<code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">create_task</code><span class="sig-paren">(</span><em class="sig-param">coro</em>, <em class="sig-param">*</em>, <em class="sig-param">name=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.create_task" title="Permalink to this definition">¶</a></dt>
<dd><p>Wrap the <em>coro</em> <a class="reference internal" href="#coroutine"><span class="std std-ref">coroutine</span></a> into a <a class="reference internal" href="#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">Task</span></code></a>
and schedule its execution.  Return the Task object.</p>
<p>If <em>name</em> is not <code class="docutils literal notranslate"><span class="pre">None</span></code>, it is set as the name of the task using
<a class="reference internal" href="#asyncio.Task.set_name" title="asyncio.Task.set_name"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Task.set_name()</span></code></a>.</p>
<p>The task is executed in the loop returned by <a class="reference internal" href="asyncio-eventloop.html#asyncio.get_running_loop" title="asyncio.get_running_loop"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_running_loop()</span></code></a>,
<a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a> is raised if there is no running loop in
current thread.</p>
<p>This function has been <strong>added in Python 3.7</strong>.  Prior to
Python 3.7, the low-level <a class="reference internal" href="asyncio-future.html#asyncio.ensure_future" title="asyncio.ensure_future"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.ensure_future()</span></code></a> function
can be used instead:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">coro</span><span class="p">():</span>
    <span class="o">...</span>

<span class="c1"># In Python 3.7+</span>
<span class="n">task</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span><span class="n">coro</span><span class="p">())</span>
<span class="o">...</span>

<span class="c1"># This works in all Python versions but is less readable</span>
<span class="n">task</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">ensure_future</span><span class="p">(</span><span class="n">coro</span><span class="p">())</span>
<span class="o">...</span>
</pre></div>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>Added the <code class="docutils literal notranslate"><span class="pre">name</span></code> parameter.</p>
</div>
</dd></dl>

</section>
<section id="sleeping">
<h2><a class="toc-backref" href="#id5">Sleeping</a><a class="headerlink" href="#sleeping" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.sleep">
<em class="property">coroutine </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">sleep</code><span class="sig-paren">(</span><em class="sig-param">delay</em>, <em class="sig-param">result=None</em>, <em class="sig-param">*</em>, <em class="sig-param">loop=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.sleep" title="Permalink to this definition">¶</a></dt>
<dd><p>Block for <em>delay</em> seconds.</p>
<p>If <em>result</em> is provided, it is returned to the caller
when the coroutine completes.</p>
<p><code class="docutils literal notranslate"><span class="pre">sleep()</span></code> always suspends the current task, allowing other tasks
to run.</p>
<p>Setting the delay to 0 provides an optimized path to allow other
tasks to run. This can be used by long-running functions to avoid
blocking the event loop for the full duration of the function call.</p>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.10: </span>The <em>loop</em> parameter.</p>
</div>
<p id="asyncio-example-sleep">Example of coroutine displaying the current date every second
for 5 seconds:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">datetime</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">display_date</span><span class="p">():</span>
    <span class="n">loop</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">get_running_loop</span><span class="p">()</span>
    <span class="n">end_time</span> <span class="o">=</span> <span class="n">loop</span><span class="o">.</span><span class="n">time</span><span class="p">()</span> <span class="o">+</span> <span class="mf">5.0</span>
    <span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
        <span class="nb">print</span><span class="p">(</span><span class="n">datetime</span><span class="o">.</span><span class="n">datetime</span><span class="o">.</span><span class="n">now</span><span class="p">())</span>
        <span class="k">if</span> <span class="p">(</span><span class="n">loop</span><span class="o">.</span><span class="n">time</span><span class="p">()</span> <span class="o">+</span> <span class="mf">1.0</span><span class="p">)</span> <span class="o">&gt;=</span> <span class="n">end_time</span><span class="p">:</span>
            <span class="k">break</span>
        <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">display_date</span><span class="p">())</span>
</pre></div>
</div>
</dd></dl>

</section>
<section id="running-tasks-concurrently">
<h2><a class="toc-backref" href="#id6">Running Tasks Concurrently</a><a class="headerlink" href="#running-tasks-concurrently" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.gather">
<em class="property">awaitable </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">gather</code><span class="sig-paren">(</span><em class="sig-param">*aws</em>, <em class="sig-param">loop=None</em>, <em class="sig-param">return_exceptions=False</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.gather" title="Permalink to this definition">¶</a></dt>
<dd><p>Run <a class="reference internal" href="#asyncio-awaitables"><span class="std std-ref">awaitable objects</span></a> in the <em>aws</em>
sequence <em>concurrently</em>.</p>
<p>If any awaitable in <em>aws</em> is a coroutine, it is automatically
scheduled as a Task.</p>
<p>If all awaitables are completed successfully, the result is an
aggregate list of returned values.  The order of result values
corresponds to the order of awaitables in <em>aws</em>.</p>
<p>If <em>return_exceptions</em> is <code class="docutils literal notranslate"><span class="pre">False</span></code> (default), the first
raised exception is immediately propagated to the task that
awaits on <code class="docutils literal notranslate"><span class="pre">gather()</span></code>.  Other awaitables in the <em>aws</em> sequence
<strong>won’t be cancelled</strong> and will continue to run.</p>
<p>If <em>return_exceptions</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code>, exceptions are treated the
same as successful results, and aggregated in the result list.</p>
<p>If <code class="docutils literal notranslate"><span class="pre">gather()</span></code> is <em>cancelled</em>, all submitted awaitables
(that have not completed yet) are also <em>cancelled</em>.</p>
<p>If any Task or Future from the <em>aws</em> sequence is <em>cancelled</em>, it is
treated as if it raised <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> – the <code class="docutils literal notranslate"><span class="pre">gather()</span></code>
call is <strong>not</strong> cancelled in this case.  This is to prevent the
cancellation of one submitted Task/Future to cause other
Tasks/Futures to be cancelled.</p>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.10: </span>The <em>loop</em> parameter.</p>
</div>
<p id="asyncio-example-gather">Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">factorial</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">number</span><span class="p">):</span>
    <span class="n">f</span> <span class="o">=</span> <span class="mi">1</span>
    <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="n">number</span> <span class="o">+</span> <span class="mi">1</span><span class="p">):</span>
        <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;Task </span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">: Compute factorial(</span><span class="si">{</span><span class="n">number</span><span class="si">}</span><span class="s2">), currently i=</span><span class="si">{</span><span class="n">i</span><span class="si">}</span><span class="s2">...&quot;</span><span class="p">)</span>
        <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
        <span class="n">f</span> <span class="o">*=</span> <span class="n">i</span>
    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;Task </span><span class="si">{</span><span class="n">name</span><span class="si">}</span><span class="s2">: factorial(</span><span class="si">{</span><span class="n">number</span><span class="si">}</span><span class="s2">) = </span><span class="si">{</span><span class="n">f</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>
    <span class="k">return</span> <span class="n">f</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Schedule three calls *concurrently*:</span>
    <span class="n">L</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">gather</span><span class="p">(</span>
        <span class="n">factorial</span><span class="p">(</span><span class="s2">&quot;A&quot;</span><span class="p">,</span> <span class="mi">2</span><span class="p">),</span>
        <span class="n">factorial</span><span class="p">(</span><span class="s2">&quot;B&quot;</span><span class="p">,</span> <span class="mi">3</span><span class="p">),</span>
        <span class="n">factorial</span><span class="p">(</span><span class="s2">&quot;C&quot;</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span>
    <span class="p">)</span>
    <span class="nb">print</span><span class="p">(</span><span class="n">L</span><span class="p">)</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>

<span class="c1"># Expected output:</span>
<span class="c1">#</span>
<span class="c1">#     Task A: Compute factorial(2), currently i=2...</span>
<span class="c1">#     Task B: Compute factorial(3), currently i=2...</span>
<span class="c1">#     Task C: Compute factorial(4), currently i=2...</span>
<span class="c1">#     Task A: factorial(2) = 2</span>
<span class="c1">#     Task B: Compute factorial(3), currently i=3...</span>
<span class="c1">#     Task C: Compute factorial(4), currently i=3...</span>
<span class="c1">#     Task B: factorial(3) = 6</span>
<span class="c1">#     Task C: Compute factorial(4), currently i=4...</span>
<span class="c1">#     Task C: factorial(4) = 24</span>
<span class="c1">#     [2, 6, 24]</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>If <em>return_exceptions</em> is False, cancelling gather() after it
has been marked done won’t cancel any submitted awaitables.
For instance, gather can be marked done after propagating an
exception to the caller, therefore, calling <code class="docutils literal notranslate"><span class="pre">gather.cancel()</span></code>
after catching an exception (raised by one of the awaitables) from
gather won’t cancel any other awaitables.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>If the <em>gather</em> itself is cancelled, the cancellation is
propagated regardless of <em>return_exceptions</em>.</p>
</div>
</dd></dl>

</section>
<section id="shielding-from-cancellation">
<h2><a class="toc-backref" href="#id7">Shielding From Cancellation</a><a class="headerlink" href="#shielding-from-cancellation" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.shield">
<em class="property">awaitable </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">shield</code><span class="sig-paren">(</span><em class="sig-param">aw</em>, <em class="sig-param">*</em>, <em class="sig-param">loop=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.shield" title="Permalink to this definition">¶</a></dt>
<dd><p>Protect an <a class="reference internal" href="#asyncio-awaitables"><span class="std std-ref">awaitable object</span></a>
from being <a class="reference internal" href="#asyncio.Task.cancel" title="asyncio.Task.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cancelled</span></code></a>.</p>
<p>If <em>aw</em> is a coroutine it is automatically scheduled as a Task.</p>
<p>The statement:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">res</span> <span class="o">=</span> <span class="k">await</span> <span class="n">shield</span><span class="p">(</span><span class="n">something</span><span class="p">())</span>
</pre></div>
</div>
<p>is equivalent to:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">res</span> <span class="o">=</span> <span class="k">await</span> <span class="n">something</span><span class="p">()</span>
</pre></div>
</div>
<p><em>except</em> that if the coroutine containing it is cancelled, the
Task running in <code class="docutils literal notranslate"><span class="pre">something()</span></code> is not cancelled.  From the point
of view of <code class="docutils literal notranslate"><span class="pre">something()</span></code>, the cancellation did not happen.
Although its caller is still cancelled, so the “await” expression
still raises a <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a>.</p>
<p>If <code class="docutils literal notranslate"><span class="pre">something()</span></code> is cancelled by other means (i.e. from within
itself) that would also cancel <code class="docutils literal notranslate"><span class="pre">shield()</span></code>.</p>
<p>If it is desired to completely ignore cancellation (not recommended)
the <code class="docutils literal notranslate"><span class="pre">shield()</span></code> function should be combined with a try/except
clause, as follows:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span>
    <span class="n">res</span> <span class="o">=</span> <span class="k">await</span> <span class="n">shield</span><span class="p">(</span><span class="n">something</span><span class="p">())</span>
<span class="k">except</span> <span class="n">CancelledError</span><span class="p">:</span>
    <span class="n">res</span> <span class="o">=</span> <span class="kc">None</span>
</pre></div>
</div>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.10: </span>The <em>loop</em> parameter.</p>
</div>
</dd></dl>

</section>
<section id="timeouts">
<h2><a class="toc-backref" href="#id8">Timeouts</a><a class="headerlink" href="#timeouts" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.wait_for">
<em class="property">coroutine </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">wait_for</code><span class="sig-paren">(</span><em class="sig-param">aw</em>, <em class="sig-param">timeout</em>, <em class="sig-param">*</em>, <em class="sig-param">loop=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.wait_for" title="Permalink to this definition">¶</a></dt>
<dd><p>Wait for the <em>aw</em> <a class="reference internal" href="#asyncio-awaitables"><span class="std std-ref">awaitable</span></a>
to complete with a timeout.</p>
<p>If <em>aw</em> is a coroutine it is automatically scheduled as a Task.</p>
<p><em>timeout</em> can either be <code class="docutils literal notranslate"><span class="pre">None</span></code> or a float or int number of seconds
to wait for.  If <em>timeout</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, block until the future
completes.</p>
<p>If a timeout occurs, it cancels the task and raises
<a class="reference internal" href="asyncio-exceptions.html#asyncio.TimeoutError" title="asyncio.TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">asyncio.TimeoutError</span></code></a>.</p>
<p>To avoid the task <a class="reference internal" href="#asyncio.Task.cancel" title="asyncio.Task.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cancellation</span></code></a>,
wrap it in <a class="reference internal" href="#asyncio.shield" title="asyncio.shield"><code class="xref py py-func docutils literal notranslate"><span class="pre">shield()</span></code></a>.</p>
<p>The function will wait until the future is actually cancelled,
so the total wait time may exceed the <em>timeout</em>. If an exception
happens during cancellation, it is propagated.</p>
<p>If the wait is cancelled, the future <em>aw</em> is also cancelled.</p>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.10: </span>The <em>loop</em> parameter.</p>
</div>
<p id="asyncio-example-waitfor">Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">eternity</span><span class="p">():</span>
    <span class="c1"># Sleep for one hour</span>
    <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">3600</span><span class="p">)</span>
    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;yay!&#39;</span><span class="p">)</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Wait for at most 1 second</span>
    <span class="k">try</span><span class="p">:</span>
        <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">wait_for</span><span class="p">(</span><span class="n">eternity</span><span class="p">(),</span> <span class="n">timeout</span><span class="o">=</span><span class="mf">1.0</span><span class="p">)</span>
    <span class="k">except</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">TimeoutError</span><span class="p">:</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;timeout!&#39;</span><span class="p">)</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>

<span class="c1"># Expected output:</span>
<span class="c1">#</span>
<span class="c1">#     timeout!</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>When <em>aw</em> is cancelled due to a timeout, <code class="docutils literal notranslate"><span class="pre">wait_for</span></code> waits
for <em>aw</em> to be cancelled.  Previously, it raised
<a class="reference internal" href="asyncio-exceptions.html#asyncio.TimeoutError" title="asyncio.TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">asyncio.TimeoutError</span></code></a> immediately.</p>
</div>
</dd></dl>

</section>
<section id="waiting-primitives">
<h2><a class="toc-backref" href="#id9">Waiting Primitives</a><a class="headerlink" href="#waiting-primitives" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.wait">
<em class="property">coroutine </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">wait</code><span class="sig-paren">(</span><em class="sig-param">aws</em>, <em class="sig-param">*</em>, <em class="sig-param">loop=None</em>, <em class="sig-param">timeout=None</em>, <em class="sig-param">return_when=ALL_COMPLETED</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.wait" title="Permalink to this definition">¶</a></dt>
<dd><p>Run <a class="reference internal" href="#asyncio-awaitables"><span class="std std-ref">awaitable objects</span></a> in the <em>aws</em>
iterable concurrently and block until the condition specified
by <em>return_when</em>.</p>
<p>The <em>aws</em> iterable must not be empty.</p>
<p>Returns two sets of Tasks/Futures: <code class="docutils literal notranslate"><span class="pre">(done,</span> <span class="pre">pending)</span></code>.</p>
<p>Usage:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">done</span><span class="p">,</span> <span class="n">pending</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">wait</span><span class="p">(</span><span class="n">aws</span><span class="p">)</span>
</pre></div>
</div>
<p><em>timeout</em> (a float or int), if specified, can be used to control
the maximum number of seconds to wait before returning.</p>
<p>Note that this function does not raise <a class="reference internal" href="asyncio-exceptions.html#asyncio.TimeoutError" title="asyncio.TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">asyncio.TimeoutError</span></code></a>.
Futures or Tasks that aren’t done when the timeout occurs are simply
returned in the second set.</p>
<p><em>return_when</em> indicates when this function should return.  It must
be one of the following constants:</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 42%" />
<col style="width: 58%" />
</colgroup>
<thead>
<tr class="row-odd"><th class="head"><p>Constant</p></th>
<th class="head"><p>Description</p></th>
</tr>
</thead>
<tbody>
<tr class="row-even"><td><p><code class="xref py py-const docutils literal notranslate"><span class="pre">FIRST_COMPLETED</span></code></p></td>
<td><p>The function will return when any
future finishes or is cancelled.</p></td>
</tr>
<tr class="row-odd"><td><p><code class="xref py py-const docutils literal notranslate"><span class="pre">FIRST_EXCEPTION</span></code></p></td>
<td><p>The function will return when any
future finishes by raising an
exception.  If no future raises an
exception then it is equivalent to
<code class="xref py py-const docutils literal notranslate"><span class="pre">ALL_COMPLETED</span></code>.</p></td>
</tr>
<tr class="row-even"><td><p><code class="xref py py-const docutils literal notranslate"><span class="pre">ALL_COMPLETED</span></code></p></td>
<td><p>The function will return when all
futures finish or are cancelled.</p></td>
</tr>
</tbody>
</table>
<p>Unlike <a class="reference internal" href="#asyncio.wait_for" title="asyncio.wait_for"><code class="xref py py-func docutils literal notranslate"><span class="pre">wait_for()</span></code></a>, <code class="docutils literal notranslate"><span class="pre">wait()</span></code> does not cancel the
futures when a timeout occurs.</p>
<div class="deprecated">
<p><span class="versionmodified deprecated">Deprecated since version 3.8: </span>If any awaitable in <em>aws</em> is a coroutine, it is automatically
scheduled as a Task.  Passing coroutines objects to
<code class="docutils literal notranslate"><span class="pre">wait()</span></code> directly is deprecated as it leads to
<a class="reference internal" href="#asyncio-example-wait-coroutine"><span class="std std-ref">confusing behavior</span></a>.</p>
</div>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.10: </span>The <em>loop</em> parameter.</p>
</div>
<div class="admonition note" id="asyncio-example-wait-coroutine">
<p class="admonition-title">Note</p>
<p><code class="docutils literal notranslate"><span class="pre">wait()</span></code> schedules coroutines as Tasks automatically and later
returns those implicitly created Task objects in <code class="docutils literal notranslate"><span class="pre">(done,</span> <span class="pre">pending)</span></code>
sets.  Therefore the following code won’t work as expected:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">foo</span><span class="p">():</span>
    <span class="k">return</span> <span class="mi">42</span>

<span class="n">coro</span> <span class="o">=</span> <span class="n">foo</span><span class="p">()</span>
<span class="n">done</span><span class="p">,</span> <span class="n">pending</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">wait</span><span class="p">({</span><span class="n">coro</span><span class="p">})</span>

<span class="k">if</span> <span class="n">coro</span> <span class="ow">in</span> <span class="n">done</span><span class="p">:</span>
    <span class="c1"># This branch will never be run!</span>
</pre></div>
</div>
<p>Here is how the above snippet can be fixed:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">foo</span><span class="p">():</span>
    <span class="k">return</span> <span class="mi">42</span>

<span class="n">task</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span><span class="n">foo</span><span class="p">())</span>
<span class="n">done</span><span class="p">,</span> <span class="n">pending</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">wait</span><span class="p">({</span><span class="n">task</span><span class="p">})</span>

<span class="k">if</span> <span class="n">task</span> <span class="ow">in</span> <span class="n">done</span><span class="p">:</span>
    <span class="c1"># Everything will work as expected now.</span>
</pre></div>
</div>
</div>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.11: </span>Passing coroutine objects to <code class="docutils literal notranslate"><span class="pre">wait()</span></code> directly is
deprecated.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="asyncio.as_completed">
<code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">as_completed</code><span class="sig-paren">(</span><em class="sig-param">aws</em>, <em class="sig-param">*</em>, <em class="sig-param">loop=None</em>, <em class="sig-param">timeout=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.as_completed" title="Permalink to this definition">¶</a></dt>
<dd><p>Run <a class="reference internal" href="#asyncio-awaitables"><span class="std std-ref">awaitable objects</span></a> in the <em>aws</em>
iterable concurrently.  Return an iterator of coroutines.
Each coroutine returned can be awaited to get the earliest next
result from the iterable of the remaining awaitables.</p>
<p>Raises <a class="reference internal" href="asyncio-exceptions.html#asyncio.TimeoutError" title="asyncio.TimeoutError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">asyncio.TimeoutError</span></code></a> if the timeout occurs before
all Futures are done.</p>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.10: </span>The <em>loop</em> parameter.</p>
</div>
<p>Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">for</span> <span class="n">coro</span> <span class="ow">in</span> <span class="n">as_completed</span><span class="p">(</span><span class="n">aws</span><span class="p">):</span>
    <span class="n">earliest_result</span> <span class="o">=</span> <span class="k">await</span> <span class="n">coro</span>
    <span class="c1"># ...</span>
</pre></div>
</div>
</dd></dl>

</section>
<section id="running-in-threads">
<h2><a class="toc-backref" href="#id10">Running in Threads</a><a class="headerlink" href="#running-in-threads" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.to_thread">
<em class="property">coroutine </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">to_thread</code><span class="sig-paren">(</span><em class="sig-param">func</em>, <em class="sig-param">/</em>, <em class="sig-param">*args</em>, <em class="sig-param">**kwargs</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.to_thread" title="Permalink to this definition">¶</a></dt>
<dd><p>Asynchronously run function <em>func</em> in a separate thread.</p>
<p>Any *args and **kwargs supplied for this function are directly passed
to <em>func</em>. Also, the current <a class="reference internal" href="contextvars.html#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">contextvars.Context</span></code></a> is propagated,
allowing context variables from the event loop thread to be accessed in the
separate thread.</p>
<p>Return a coroutine that can be awaited to get the eventual result of <em>func</em>.</p>
<p>This coroutine function is primarily intended to be used for executing
IO-bound functions/methods that would otherwise block the event loop if
they were ran in the main thread. For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">blocking_io</span><span class="p">():</span>
    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;start blocking_io at </span><span class="si">{</span><span class="n">time</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%X</span><span class="s1">&#39;</span><span class="p">)</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>
    <span class="c1"># Note that time.sleep() can be replaced with any blocking</span>
    <span class="c1"># IO-bound operation, such as file operations.</span>
    <span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;blocking_io complete at </span><span class="si">{</span><span class="n">time</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%X</span><span class="s1">&#39;</span><span class="p">)</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;started main at </span><span class="si">{</span><span class="n">time</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%X</span><span class="s1">&#39;</span><span class="p">)</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>

    <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">gather</span><span class="p">(</span>
        <span class="n">asyncio</span><span class="o">.</span><span class="n">to_thread</span><span class="p">(</span><span class="n">blocking_io</span><span class="p">),</span>
        <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">))</span>

    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s2">&quot;finished main at </span><span class="si">{</span><span class="n">time</span><span class="o">.</span><span class="n">strftime</span><span class="p">(</span><span class="s1">&#39;</span><span class="si">%X</span><span class="s1">&#39;</span><span class="p">)</span><span class="si">}</span><span class="s2">&quot;</span><span class="p">)</span>


<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>

<span class="c1"># Expected output:</span>
<span class="c1">#</span>
<span class="c1"># started main at 19:50:53</span>
<span class="c1"># start blocking_io at 19:50:53</span>
<span class="c1"># blocking_io complete at 19:50:54</span>
<span class="c1"># finished main at 19:50:54</span>
</pre></div>
</div>
<p>Directly calling <cite>blocking_io()</cite> in any coroutine would block the event loop
for its duration, resulting in an additional 1 second of run time. Instead,
by using <cite>asyncio.to_thread()</cite>, we can run it in a separate thread without
blocking the event loop.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Due to the <a class="reference internal" href="../glossary.html#term-gil"><span class="xref std std-term">GIL</span></a>, <cite>asyncio.to_thread()</cite> can typically only be used
to make IO-bound functions non-blocking. However, for extension modules
that release the GIL or alternative Python implementations that don’t
have one, <cite>asyncio.to_thread()</cite> can also be used for CPU-bound functions.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.9.</span></p>
</div>
</dd></dl>

</section>
<section id="scheduling-from-other-threads">
<h2><a class="toc-backref" href="#id11">Scheduling From Other Threads</a><a class="headerlink" href="#scheduling-from-other-threads" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.run_coroutine_threadsafe">
<code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">run_coroutine_threadsafe</code><span class="sig-paren">(</span><em class="sig-param">coro</em>, <em class="sig-param">loop</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.run_coroutine_threadsafe" title="Permalink to this definition">¶</a></dt>
<dd><p>Submit a coroutine to the given event loop.  Thread-safe.</p>
<p>Return a <a class="reference internal" href="concurrent.futures.html#concurrent.futures.Future" title="concurrent.futures.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">concurrent.futures.Future</span></code></a> to wait for the result
from another OS thread.</p>
<p>This function is meant to be called from a different OS thread
than the one where the event loop is running.  Example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="c1"># Create a coroutine</span>
<span class="n">coro</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="n">result</span><span class="o">=</span><span class="mi">3</span><span class="p">)</span>

<span class="c1"># Submit the coroutine to a given loop</span>
<span class="n">future</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">run_coroutine_threadsafe</span><span class="p">(</span><span class="n">coro</span><span class="p">,</span> <span class="n">loop</span><span class="p">)</span>

<span class="c1"># Wait for the result with an optional timeout argument</span>
<span class="k">assert</span> <span class="n">future</span><span class="o">.</span><span class="n">result</span><span class="p">(</span><span class="n">timeout</span><span class="p">)</span> <span class="o">==</span> <span class="mi">3</span>
</pre></div>
</div>
<p>If an exception is raised in the coroutine, the returned Future
will be notified.  It can also be used to cancel the task in
the event loop:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">try</span><span class="p">:</span>
    <span class="n">result</span> <span class="o">=</span> <span class="n">future</span><span class="o">.</span><span class="n">result</span><span class="p">(</span><span class="n">timeout</span><span class="p">)</span>
<span class="k">except</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">TimeoutError</span><span class="p">:</span>
    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;The coroutine took too long, cancelling the task...&#39;</span><span class="p">)</span>
    <span class="n">future</span><span class="o">.</span><span class="n">cancel</span><span class="p">()</span>
<span class="k">except</span> <span class="ne">Exception</span> <span class="k">as</span> <span class="n">exc</span><span class="p">:</span>
    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;The coroutine raised an exception: </span><span class="si">{</span><span class="n">exc</span><span class="si">!r}</span><span class="s1">&#39;</span><span class="p">)</span>
<span class="k">else</span><span class="p">:</span>
    <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;The coroutine returned: </span><span class="si">{</span><span class="n">result</span><span class="si">!r}</span><span class="s1">&#39;</span><span class="p">)</span>
</pre></div>
</div>
<p>See the <a class="reference internal" href="asyncio-dev.html#asyncio-multithreading"><span class="std std-ref">concurrency and multithreading</span></a>
section of the documentation.</p>
<p>Unlike other asyncio functions this function requires the <em>loop</em>
argument to be passed explicitly.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.1.</span></p>
</div>
</dd></dl>

</section>
<section id="introspection">
<h2><a class="toc-backref" href="#id12">Introspection</a><a class="headerlink" href="#introspection" title="Permalink to this headline">¶</a></h2>
<dl class="function">
<dt id="asyncio.current_task">
<code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">current_task</code><span class="sig-paren">(</span><em class="sig-param">loop=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.current_task" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the currently running <a class="reference internal" href="#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">Task</span></code></a> instance, or <code class="docutils literal notranslate"><span class="pre">None</span></code> if
no task is running.</p>
<p>If <em>loop</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> <a class="reference internal" href="asyncio-eventloop.html#asyncio.get_running_loop" title="asyncio.get_running_loop"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_running_loop()</span></code></a> is used to get
the current loop.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
</dd></dl>

<dl class="function">
<dt id="asyncio.all_tasks">
<code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">all_tasks</code><span class="sig-paren">(</span><em class="sig-param">loop=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.all_tasks" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a set of not yet finished <a class="reference internal" href="#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">Task</span></code></a> objects run by
the loop.</p>
<p>If <em>loop</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, <a class="reference internal" href="asyncio-eventloop.html#asyncio.get_running_loop" title="asyncio.get_running_loop"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_running_loop()</span></code></a> is used for getting
current loop.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7.</span></p>
</div>
</dd></dl>

</section>
<section id="task-object">
<h2><a class="toc-backref" href="#id13">Task Object</a><a class="headerlink" href="#task-object" title="Permalink to this headline">¶</a></h2>
<dl class="class">
<dt id="asyncio.Task">
<em class="property">class </em><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">Task</code><span class="sig-paren">(</span><em class="sig-param">coro</em>, <em class="sig-param">*</em>, <em class="sig-param">loop=None</em>, <em class="sig-param">name=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task" title="Permalink to this definition">¶</a></dt>
<dd><p>A <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future-like</span></code></a> object that runs a Python
<a class="reference internal" href="#coroutine"><span class="std std-ref">coroutine</span></a>.  Not thread-safe.</p>
<p>Tasks are used to run coroutines in event loops.
If a coroutine awaits on a Future, the Task suspends
the execution of the coroutine and waits for the completion
of the Future.  When the Future is <em>done</em>, the execution of
the wrapped coroutine resumes.</p>
<p>Event loops use cooperative scheduling: an event loop runs
one Task at a time.  While a Task awaits for the completion of a
Future, the event loop runs other Tasks, callbacks, or performs
IO operations.</p>
<p>Use the high-level <a class="reference internal" href="#asyncio.create_task" title="asyncio.create_task"><code class="xref py py-func docutils literal notranslate"><span class="pre">asyncio.create_task()</span></code></a> function to create
Tasks, or the low-level <a class="reference internal" href="asyncio-eventloop.html#asyncio.loop.create_task" title="asyncio.loop.create_task"><code class="xref py py-meth docutils literal notranslate"><span class="pre">loop.create_task()</span></code></a> or
<a class="reference internal" href="asyncio-future.html#asyncio.ensure_future" title="asyncio.ensure_future"><code class="xref py py-func docutils literal notranslate"><span class="pre">ensure_future()</span></code></a> functions.  Manual instantiation of Tasks
is discouraged.</p>
<p>To cancel a running Task use the <a class="reference internal" href="#asyncio.Task.cancel" title="asyncio.Task.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cancel()</span></code></a> method.  Calling it
will cause the Task to throw a <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> exception into
the wrapped coroutine.  If a coroutine is awaiting on a Future
object during cancellation, the Future object will be cancelled.</p>
<p><a class="reference internal" href="#asyncio.Task.cancelled" title="asyncio.Task.cancelled"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cancelled()</span></code></a> can be used to check if the Task was cancelled.
The method returns <code class="docutils literal notranslate"><span class="pre">True</span></code> if the wrapped coroutine did not
suppress the <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> exception and was actually
cancelled.</p>
<p><a class="reference internal" href="#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">asyncio.Task</span></code></a> inherits from <a class="reference internal" href="asyncio-future.html#asyncio.Future" title="asyncio.Future"><code class="xref py py-class docutils literal notranslate"><span class="pre">Future</span></code></a> all of its
APIs except <a class="reference internal" href="asyncio-future.html#asyncio.Future.set_result" title="asyncio.Future.set_result"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.set_result()</span></code></a> and
<a class="reference internal" href="asyncio-future.html#asyncio.Future.set_exception" title="asyncio.Future.set_exception"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.set_exception()</span></code></a>.</p>
<p>Tasks support the <a class="reference internal" href="contextvars.html#module-contextvars" title="contextvars: Context Variables"><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextvars</span></code></a> module.  When a Task
is created it copies the current context and later runs its
coroutine in the copied context.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.7: </span>Added support for the <a class="reference internal" href="contextvars.html#module-contextvars" title="contextvars: Context Variables"><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextvars</span></code></a> module.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.8: </span>Added the <code class="docutils literal notranslate"><span class="pre">name</span></code> parameter.</p>
</div>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.10: </span>The <em>loop</em> parameter.</p>
</div>
<dl class="method">
<dt id="asyncio.Task.cancel">
<code class="sig-name descname">cancel</code><span class="sig-paren">(</span><em class="sig-param">msg=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.cancel" title="Permalink to this definition">¶</a></dt>
<dd><p>Request the Task to be cancelled.</p>
<p>This arranges for a <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> exception to be thrown
into the wrapped coroutine on the next cycle of the event loop.</p>
<p>The coroutine then has a chance to clean up or even deny the
request by suppressing the exception with a <a class="reference internal" href="../reference/compound_stmts.html#try"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">try</span></code></a> …
… <code class="docutils literal notranslate"><span class="pre">except</span> <span class="pre">CancelledError</span></code> … <a class="reference internal" href="../reference/compound_stmts.html#finally"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">finally</span></code></a> block.
Therefore, unlike <a class="reference internal" href="asyncio-future.html#asyncio.Future.cancel" title="asyncio.Future.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.cancel()</span></code></a>, <a class="reference internal" href="#asyncio.Task.cancel" title="asyncio.Task.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Task.cancel()</span></code></a> does
not guarantee that the Task will be cancelled, although
suppressing cancellation completely is not common and is actively
discouraged.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.9: </span>Added the <code class="docutils literal notranslate"><span class="pre">msg</span></code> parameter.</p>
</div>
<p id="asyncio-example-task-cancel">The following example illustrates how coroutines can intercept
the cancellation request:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">async</span> <span class="k">def</span> <span class="nf">cancel_me</span><span class="p">():</span>
    <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;cancel_me(): before sleep&#39;</span><span class="p">)</span>

    <span class="k">try</span><span class="p">:</span>
        <span class="c1"># Wait for 1 hour</span>
        <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">3600</span><span class="p">)</span>
    <span class="k">except</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">CancelledError</span><span class="p">:</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;cancel_me(): cancel sleep&#39;</span><span class="p">)</span>
        <span class="k">raise</span>
    <span class="k">finally</span><span class="p">:</span>
        <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;cancel_me(): after sleep&#39;</span><span class="p">)</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="c1"># Create a &quot;cancel_me&quot; Task</span>
    <span class="n">task</span> <span class="o">=</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">create_task</span><span class="p">(</span><span class="n">cancel_me</span><span class="p">())</span>

    <span class="c1"># Wait for 1 second</span>
    <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>

    <span class="n">task</span><span class="o">.</span><span class="n">cancel</span><span class="p">()</span>
    <span class="k">try</span><span class="p">:</span>
        <span class="k">await</span> <span class="n">task</span>
    <span class="k">except</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">CancelledError</span><span class="p">:</span>
        <span class="nb">print</span><span class="p">(</span><span class="s2">&quot;main(): cancel_me is cancelled now&quot;</span><span class="p">)</span>

<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>

<span class="c1"># Expected output:</span>
<span class="c1">#</span>
<span class="c1">#     cancel_me(): before sleep</span>
<span class="c1">#     cancel_me(): cancel sleep</span>
<span class="c1">#     cancel_me(): after sleep</span>
<span class="c1">#     main(): cancel_me is cancelled now</span>
</pre></div>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.cancelled">
<code class="sig-name descname">cancelled</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.cancelled" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the Task is <em>cancelled</em>.</p>
<p>The Task is <em>cancelled</em> when the cancellation was requested with
<a class="reference internal" href="#asyncio.Task.cancel" title="asyncio.Task.cancel"><code class="xref py py-meth docutils literal notranslate"><span class="pre">cancel()</span></code></a> and the wrapped coroutine propagated the
<a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> exception thrown into it.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.done">
<code class="sig-name descname">done</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.done" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the Task is <em>done</em>.</p>
<p>A Task is <em>done</em> when the wrapped coroutine either returned
a value, raised an exception, or the Task was cancelled.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.result">
<code class="sig-name descname">result</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.result" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the result of the Task.</p>
<p>If the Task is <em>done</em>, the result of the wrapped coroutine
is returned (or if the coroutine raised an exception, that
exception is re-raised.)</p>
<p>If the Task has been <em>cancelled</em>, this method raises
a <a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> exception.</p>
<p>If the Task’s result isn’t yet available, this method raises
a <a class="reference internal" href="asyncio-exceptions.html#asyncio.InvalidStateError" title="asyncio.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">InvalidStateError</span></code></a> exception.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.exception">
<code class="sig-name descname">exception</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.exception" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the exception of the Task.</p>
<p>If the wrapped coroutine raised an exception that exception
is returned.  If the wrapped coroutine returned normally
this method returns <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
<p>If the Task has been <em>cancelled</em>, this method raises a
<a class="reference internal" href="asyncio-exceptions.html#asyncio.CancelledError" title="asyncio.CancelledError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">CancelledError</span></code></a> exception.</p>
<p>If the Task isn’t <em>done</em> yet, this method raises an
<a class="reference internal" href="asyncio-exceptions.html#asyncio.InvalidStateError" title="asyncio.InvalidStateError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">InvalidStateError</span></code></a> exception.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.add_done_callback">
<code class="sig-name descname">add_done_callback</code><span class="sig-paren">(</span><em class="sig-param">callback</em>, <em class="sig-param">*</em>, <em class="sig-param">context=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.add_done_callback" title="Permalink to this definition">¶</a></dt>
<dd><p>Add a callback to be run when the Task is <em>done</em>.</p>
<p>This method should only be used in low-level callback-based code.</p>
<p>See the documentation of <a class="reference internal" href="asyncio-future.html#asyncio.Future.add_done_callback" title="asyncio.Future.add_done_callback"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.add_done_callback()</span></code></a>
for more details.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.remove_done_callback">
<code class="sig-name descname">remove_done_callback</code><span class="sig-paren">(</span><em class="sig-param">callback</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.remove_done_callback" title="Permalink to this definition">¶</a></dt>
<dd><p>Remove <em>callback</em> from the callbacks list.</p>
<p>This method should only be used in low-level callback-based code.</p>
<p>See the documentation of <a class="reference internal" href="asyncio-future.html#asyncio.Future.remove_done_callback" title="asyncio.Future.remove_done_callback"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Future.remove_done_callback()</span></code></a>
for more details.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.get_stack">
<code class="sig-name descname">get_stack</code><span class="sig-paren">(</span><em class="sig-param">*</em>, <em class="sig-param">limit=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.get_stack" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the list of stack frames for this Task.</p>
<p>If the wrapped coroutine is not done, this returns the stack
where it is suspended.  If the coroutine has completed
successfully or was cancelled, this returns an empty list.
If the coroutine was terminated by an exception, this returns
the list of traceback frames.</p>
<p>The frames are always ordered from oldest to newest.</p>
<p>Only one stack frame is returned for a suspended coroutine.</p>
<p>The optional <em>limit</em> argument sets the maximum number of frames
to return; by default all available frames are returned.
The ordering of the returned list differs depending on whether
a stack or a traceback is returned: the newest frames of a
stack are returned, but the oldest frames of a traceback are
returned.  (This matches the behavior of the traceback module.)</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.print_stack">
<code class="sig-name descname">print_stack</code><span class="sig-paren">(</span><em class="sig-param">*</em>, <em class="sig-param">limit=None</em>, <em class="sig-param">file=None</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.print_stack" title="Permalink to this definition">¶</a></dt>
<dd><p>Print the stack or traceback for this Task.</p>
<p>This produces output similar to that of the traceback module
for the frames retrieved by <a class="reference internal" href="#asyncio.Task.get_stack" title="asyncio.Task.get_stack"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get_stack()</span></code></a>.</p>
<p>The <em>limit</em> argument is passed to <a class="reference internal" href="#asyncio.Task.get_stack" title="asyncio.Task.get_stack"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get_stack()</span></code></a> directly.</p>
<p>The <em>file</em> argument is an I/O stream to which the output
is written; by default output is written to <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stderr</span></code></a>.</p>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.get_coro">
<code class="sig-name descname">get_coro</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.get_coro" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the coroutine object wrapped by the <a class="reference internal" href="#asyncio.Task" title="asyncio.Task"><code class="xref py py-class docutils literal notranslate"><span class="pre">Task</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.8.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.get_name">
<code class="sig-name descname">get_name</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.get_name" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the name of the Task.</p>
<p>If no name has been explicitly assigned to the Task, the default
asyncio Task implementation generates a default name during
instantiation.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.8.</span></p>
</div>
</dd></dl>

<dl class="method">
<dt id="asyncio.Task.set_name">
<code class="sig-name descname">set_name</code><span class="sig-paren">(</span><em class="sig-param">value</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.Task.set_name" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the name of the Task.</p>
<p>The <em>value</em> argument can be any object, which is then
converted to a string.</p>
<p>In the default Task implementation, the name will be visible
in the <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> output of a task object.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.8.</span></p>
</div>
</dd></dl>

</dd></dl>

</section>
<section id="generator-based-coroutines">
<span id="asyncio-generator-based-coro"></span><h2><a class="toc-backref" href="#id14">Generator-based Coroutines</a><a class="headerlink" href="#generator-based-coroutines" title="Permalink to this headline">¶</a></h2>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Support for generator-based coroutines is <strong>deprecated</strong> and
is scheduled for removal in Python 3.10.</p>
</div>
<p>Generator-based coroutines predate async/await syntax.  They are
Python generators that use <code class="docutils literal notranslate"><span class="pre">yield</span> <span class="pre">from</span></code> expressions to await
on Futures and other coroutines.</p>
<p>Generator-based coroutines should be decorated with
<a class="reference internal" href="#asyncio.coroutine" title="asyncio.coroutine"><code class="xref py py-func docutils literal notranslate"><span class="pre">&#64;asyncio.coroutine</span></code></a>, although this is not
enforced.</p>
<dl class="function">
<dt id="asyncio.coroutine">
<code class="sig-prename descclassname">&#64;</code><code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">coroutine</code><a class="headerlink" href="#asyncio.coroutine" title="Permalink to this definition">¶</a></dt>
<dd><p>Decorator to mark generator-based coroutines.</p>
<p>This decorator enables legacy generator-based coroutines to be
compatible with async/await code:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="nd">@asyncio</span><span class="o">.</span><span class="n">coroutine</span>
<span class="k">def</span> <span class="nf">old_style_coroutine</span><span class="p">():</span>
    <span class="k">yield from</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>

<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
    <span class="k">await</span> <span class="n">old_style_coroutine</span><span class="p">()</span>
</pre></div>
</div>
<p>This decorator should not be used for <a class="reference internal" href="../reference/compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a>
coroutines.</p>
<div class="deprecated-removed">
<p><span class="versionmodified">Deprecated since version 3.8, will be removed in version 3.10: </span>Use <a class="reference internal" href="../reference/compound_stmts.html#async-def"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">async</span> <span class="pre">def</span></code></a> instead.</p>
</div>
</dd></dl>

<dl class="function">
<dt id="asyncio.iscoroutine">
<code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">iscoroutine</code><span class="sig-paren">(</span><em class="sig-param">obj</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.iscoroutine" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if <em>obj</em> is a <a class="reference internal" href="#coroutine"><span class="std std-ref">coroutine object</span></a>.</p>
<p>This method is different from <a class="reference internal" href="inspect.html#inspect.iscoroutine" title="inspect.iscoroutine"><code class="xref py py-func docutils literal notranslate"><span class="pre">inspect.iscoroutine()</span></code></a> because
it returns <code class="docutils literal notranslate"><span class="pre">True</span></code> for generator-based coroutines.</p>
</dd></dl>

<dl class="function">
<dt id="asyncio.iscoroutinefunction">
<code class="sig-prename descclassname">asyncio.</code><code class="sig-name descname">iscoroutinefunction</code><span class="sig-paren">(</span><em class="sig-param">func</em><span class="sig-paren">)</span><a class="headerlink" href="#asyncio.iscoroutinefunction" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if <em>func</em> is a <a class="reference internal" href="#coroutine"><span class="std std-ref">coroutine function</span></a>.</p>
<p>This method is different from <a class="reference internal" href="inspect.html#inspect.iscoroutinefunction" title="inspect.iscoroutinefunction"><code class="xref py py-func docutils literal notranslate"><span class="pre">inspect.iscoroutinefunction()</span></code></a>
because it returns <code class="docutils literal notranslate"><span class="pre">True</span></code> for generator-based coroutine functions
decorated with <a class="reference internal" href="#asyncio.coroutine" title="asyncio.coroutine"><code class="xref py py-func docutils literal notranslate"><span class="pre">&#64;coroutine</span></code></a>.</p>
</dd></dl>

</section>
</section>


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  <h3><a href="../contents.html">Table of Contents</a></h3>
  <ul>
<li><a class="reference internal" href="#">Coroutines and Tasks</a><ul>
<li><a class="reference internal" href="#coroutines">Coroutines</a></li>
<li><a class="reference internal" href="#awaitables">Awaitables</a></li>
<li><a class="reference internal" href="#running-an-asyncio-program">Running an asyncio Program</a></li>
<li><a class="reference internal" href="#creating-tasks">Creating Tasks</a></li>
<li><a class="reference internal" href="#sleeping">Sleeping</a></li>
<li><a class="reference internal" href="#running-tasks-concurrently">Running Tasks Concurrently</a></li>
<li><a class="reference internal" href="#shielding-from-cancellation">Shielding From Cancellation</a></li>
<li><a class="reference internal" href="#timeouts">Timeouts</a></li>
<li><a class="reference internal" href="#waiting-primitives">Waiting Primitives</a></li>
<li><a class="reference internal" href="#running-in-threads">Running in Threads</a></li>
<li><a class="reference internal" href="#scheduling-from-other-threads">Scheduling From Other Threads</a></li>
<li><a class="reference internal" href="#introspection">Introspection</a></li>
<li><a class="reference internal" href="#task-object">Task Object</a></li>
<li><a class="reference internal" href="#generator-based-coroutines">Generator-based Coroutines</a></li>
</ul>
</li>
</ul>

  <h4>Previous topic</h4>
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